FIGURE 3.2 Estimate of HIV infections in adults as of late 1992. Source: World Health Organization, 1993.

The ultimate goal of current AIDS research is to extricate the virus from the immune system without causing further damage. To do that scientists over the past decade have focused on the complex relationship between the virus and the cells of the immune system as well as relationships of the different immune cells to each other.


A famous scientist once defined a virus as "a bit of bad news wrapped in protein." Indeed, while the experimental study of viruses can unlock a wealth of scientific information, viruses offer little else of value to human beings. Unlike the occasional bacterial species that can provide a beneficial service to humans (e.g., bacteria found lining the human intestines that aid digestion), viruses are never Good Samaritans. They seem perfectly willing to take up residence in the human body without doing anything to earn their keep.

But the scientist's comment also touched on the very simple structure of a virus. Compared with the complexity of the mammalian or bacterial cell, viruses are remarkably minimal. Most viruses are

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